1. Field of the Invention
This invention relates to a novel procedure for the azidochlorination or diazidization of glycals.
2. Information Disclosure Statement
Numerous antigens of clinical significance bear carbohydrate determinants. The blood group precursor Thomsen-Friedenreich (TF) and Tn-antigens are considered to be carcinoma markers. These antigens are synthesized intracellularly and then covered by covalently-linked carbohydrates. Both are found in the unmasked immunoreactive form on the external surface membranes of most primary carcinomas and their metastases (&gt;90% of human carcinomas). As cancer markers, TF and Tn permit early immunohistochemical detection and prognostication of the invasiveness of some carcinoma. It has been shown by Springer, et al., that these antigens are not found in sarcomas, malignant tumors of the CNS, benign tumors, and tissues with non-carcinomas disease (Springer, et al., Naturewissen--schajten, 61, 457-458, 1974).
There is thus considerable interest in preparing these and other carbohydrate determinants synthetically for use as haptens. Joined to suitable carriers, these molecules become synthetic immunogens, as well.
It is known that glycals, and more particularly galactals, may participate in addition reactions with suitable reagents, such as IN.sub.3, CIN.sub.3, ICl, (SCN).sub.2 and Cl--NH--O--C(O)R. See Brimacombe, et al., Chem. Comm. 1401 (1968); Igarashi, et al., J. Org. Chem. 32: 2521-30 (1967); Lessard, et al., Tetrahedron Lett., 56: 4887-90 (1970); Bovin, et al., Carbohydr. Res., 98: 25-35 (1981). The reagent adds at carbons 1 and 2. (The carbons at positions 3, 5 and 6 are protected, usually by benzyl or acetyl groups.) Bovin, et al. (1981), while reporting the addition of azidochloride to 3,4,6,-tri-O-acetyl-D-galactal and to 3,4,6-tri-O-benzyl-D-galactal under photolytic conditions, were unable to actually isolate the azidochloride derivative. However, they converted the crude product first into an azido-acetate derivative and then into an azido-bromide derivative, both of which were isolated.
Known techniques of preparing the desired 2-azido glycosyl chlorides are unsatisfactory. Paulsen, et al., Chem. Ber. III: 2358-69 (1978) described a ten-step procedure for the synthesis of 6-O-acetyl-2-azido-3,4-di-O-benzyl-2-deoxy-beta-D-galactopryanosyl chloride. This complicated approach did not win favor.
Lemieux, et al. Can. J. Chem. 57: 1244-51 (1979) and U.S. Pat. Nos. 4,308,376; 4,362,720 and 4,195,174 recommended a two step procedure in which an O-protected glycal was azidonitrated and the azidonitrate group was subsequently displaced by chloride (from tetraethylammonium chloride). At both stages, column chromatography was necessary to isolate the desired compound. In the method reported by Lemieux, et al., azidonitration of tri-O-acetylgalactal provided 53% of 3,4,6-tri-O-acetyl-2-azido-2-deoxy-beta-D-galactopyranosylol nitrate, 22% of 3,4,6-tri-O-acetyl-2-azido-2-deoxy-alpha-D-galactopyranosyl nitrate, 8% of the talo isomer and 5% of N-acetyl-3,4,6-tri-O-acetyl-2-azido-2-deoxy-alpha-O-galactopyranosylamine. In addition to these products, the hydrolyzed product will also be formed. The last two derivatives are the undesirable by-products which need to be separated. Thus, the azidonitration approach necessitates extensive separation of the products by liquid chromatography.
Bovin, et al., Carbohydr. Res. 98: 25-35 (1981) taught the addition of azidochloride to 3,4,6-tri-O-acetyl-D-galactal under UV irradiation. Azidochloride is highly explosive. See Chemical Abstract, 49: 7248g; Id., 55: 21944i. Lemieux, Can. J. Chem., 57: 1244, 1245 (1979) considered use of this reagent to induce free radical addition, but abandoned this approach "when a reaction involving chloroazide and with sulfuryl chloride as the radical initiator detonated with violence." Moreover, the use of UV irradiation meant that the chemist had to employ expensive quartz vessels (which transmit UV) and provide UV equipment. (Absent UV light, the reaction was greatly prolonged.)
Galli, et al., Org. Prep. and Proceed, Int., 3(5): 227-30 (1971) reported that alpha-chloro-beta-azidoethylbenzene could be prepared from styrene by reaction with FeCl.sub.3.6H.sub.2 O, NaN.sub.3, FeSO.sub.4.7H.sub.2 O, and (NH.sub.4).sub.2 S.sub.2 O.sub.8 (ammonium peroxydisulphate). Galli's procedure has not been used to azidochlorinate vinylic ethers such as O-protected-D-glycals.